High-resolution techniques for surface analysis such as atomic force microscopy (AFM) and scanning tunneling microscopy (STM) have achieved great importance in recent years, particularly in the high-resolution investigation of semiconductor wafers. Such techniques rely on the interaction between a sharp tip and the surface of an underlying specimen. The topography of a specimen can easily be surveyed, or locally resolved bonding conditions, for example of macromolecules, can be disclosed. With AFM and STM, resolutions down to the nanometer or sub nanometer range may be attained. Due to the high sensitivity of such techniques, the actual resolving ability of AFM and STM instruments depends strongly on external effects from the surroundings. Examples of such external effects include mechanical vibrations, for example, air vibrations or also bodily vibrations in the instrument or a support for the specimen, which can be produced, e.g., by movements of the building. Vibrations decrease signal to noise ratio. The high resolution of the devices can thus be only used when the disturbing effect is sufficiently reduced or compensated for.
In the prior art, active or passive vibration damping or vibration isolating devices have been used. However, such devices are often very expensive. Furthermore, particularly at very low disturbing frequencies, such as can arise, for example, from temperature instability, these devices offer only a limited protection.
U.S. Pat. No. 6,308,557 to Heiland describes a technique for compensation of vibration in a scanning microscope. Heiland's microscope, which scans in a raster mode, includes a sensor that senses mechanical vibrations and drives a filter whose output is connected to an adder together with the output of the device for producing a signal for adjusting the distance between a specimen and a scanning sensor. The output of the adder controls a device that changes the distance between the specimen and a signal sensor on the microscope head to compensate for the disturbing effects of mechanical vibrations on the signal sensor.
Although the above-described prior art technique works reasonably well in compensating for vibration, it suffers from certain drawbacks that limit its performance in lower frequencies changes such as temperature-induced drift. Thus, there is a need in the art, for a vibration compensation technique that overcomes these disadvantages.